Intrusion detection using a conductive material

ABSTRACT

Tampering with an assembly that includes an integrated circuit is detected by measuring a change in at least one property of a conductive molding formed over at least a portion of the integrated circuit. For example, the conductive molding can be a mixture of resin with conductive powder and/or fibers. The molding can be formed as a continuous region or as strips of conductive material. Conductive contacts are positioned to provide and receive current through portions of the conductive material. For example, the property of the molding can be an impedance of a portion of the conductive molding. A significant change in the impedance measured through one or more conductive contacts indicates tampering with the assembly.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of, and claims priority under 35U.S.C. §120 from, nonprovisional U.S. patent application Ser. No.11/731,423 entitled “Intrusion Detection Using A Conductive Material,”filed on Mar. 30, 2007, now U.S. Pat. No. ______ the subject matter ofwhich is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to techniques for detecting access to anintegrated circuit device.

BACKGROUND

Point of sale (POS) terminals allow customers to make payments using avariety of payment instruments, such as credit cards, debit cards, smartcards and ATM cards. To ensure that the payment information transmittedfrom the POS terminals to a payment center is not accessed byunauthorized recipients, this information is typically encrypted andsecured (e.g., using digital authentication) during transmission.However, confidential payment information entered by the user into thePOS terminal could still be intercepted by tampering with the integratedcircuits of the POS terminal. Thieves can use such informationfraudulently to receive payment. It may also be desirable to maintainconfidentiality of integrated circuit device layouts to prevent thievesfrom copying integrated circuit designs. Clearly the need to preventunauthorized access to integrated circuits is present.

U.S. Pat. No. 4,811,288 describes a technique to prevent unauthorizedaccess to a memory device through the use of a conductive mesh outsideof the memory device. To access the memory device, a thief must cutthrough the conductive mesh. Cutting through the mesh, however, altersthe conductive properties of the mesh. Altering portions of theconductive mesh can change impedances, create short circuits, and/orcreate open circuits. Detection of a change in an impedance, shortcircuits and/or open circuits is associated with tampering and in turncauses the memory to become erased. Thereby, unauthorized access tomemory is prevented. However, use of such a mesh wire bond cage isexpensive. Purchasers of integrated circuits are often very costsensitive.

SUMMARY

In one embodiment, an apparatus includes an integrated circuit deviceand a conductive region formed over the integrated circuit device. Anindication of access to the integrated circuit device can be based inpart on measurement of a change of at least one property of theconductive region. In one implementation, the measured property is animpedance of a portion within the region. In one implementation, theconductive region includes conductive powder and/or conductive fibersinterspersed within resin.

In another embodiment, a method indicates access to an integratedcircuit device based in part on a change to a property of a regionmolded over the integrated circuit device. In one implementation,indicating access includes measuring an impedance through a portion ofthe region, comparing the measured impedance with a reference impedancevalue for the portion, and indicating an access based on a substantialdifference between the measured impedance and the reference impedancevalue for the portion. In one implementation, the region includesconductive material interspersed among resin.

Other embodiments and advantages are described in the detaileddescription below. This summary does not purport to define theinventions. The inventions are defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 is a simplified cross-sectional diagram of an assembly, inaccordance with an embodiment of the present invention.

FIG. 2A is a simplified top-down view of the assembly of FIG. 1.

FIG. 2B is a simplified top-down view of an assembly with conductivematerial provided in strips, in accordance with an embodiment of thepresent invention.

FIG. 3 is a simplified cross-sectional diagram of an assembly withconductive material provided in criss crossing strips for use to detectaccess to the integrated circuit, in accordance with an embodiment ofthe present invention.

FIG. 4 is a simplified top-down view of the assembly of FIG. 3.

FIG. 5 depicts a simplified cross-sectional diagram of an assemblyincluding an integrated circuit with a conductive plate provided for useto detect access to the integrated circuit.

FIG. 6 depicts a simplified cross-sectional diagram of an assemblyincluding an integrated circuit with a conductive material provided todetect access to the integrated circuit.

FIG. 7 is a simplified cross-sectional view of point of sale device.

FIG. 8 is a flowchart of a method that can be used to detect access toan integrated circuit in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 is a simplified cross-sectional diagram of an assembly 10including an integrated circuit 11 mounted in a ball grid array (BGA)package (also known as “substrate”) 12, in accordance with an embodimentof the present invention. In one example, integrated circuit 11 is aprogrammable logic device (PLD) die that is mounted face-side down on aninside upper surface 13 of package 12 in a flip-chip manner. The term“face side” used here denotes the side of the die that receives the bulkof semiconductor processing such that circuitry is fabricated on thatface side of the die. Microbumps 14 are present in an array on a bottomface-side surface 15 of integrated circuit 11. In one example, eachmicrobump 14 is approximately 100 microns in diameter and is made ofsolder. Each microbump in the array of microbumps 14 contacts acorresponding landing pad in an array of landing pads 16 on inside uppersurface 13 of package 12. The circuitry of integrated circuit 11 iscoupled through package 12 to a printed circuit board (not shown) viasolder balls 18 on the bottom surface of package 12. Vias are providedin package 12 to conductively couple the landings for the microbumpswith solder balls 18.

An insulating material 20 is formed over integrated circuit 11. In oneexample, the insulating material is plastic or rubber. Conductivematerial 22 is formed over insulating material 20. Conductive material22 is formed as a continuous region over insulating region 20. Anindication that tampering with integrated circuit 11 has occurred isbased in part on measuring a change of at least one property ofconductive material 22. In one example, conductive material 22 is aresin-based material including conductive materials such as conductivepowder, conductive fibers and/or carbon nanotubes. For example, theconductive resin-based material is a mixture as described in U.S. PatentApplication Publication No. 2004/0217472, filed Apr. 14, 2004, byinventors Aisenbrey and Larsen. For example, conductive material 22 is aconductive ElectriPlast™ thermoplastic from Integral Technologies. Inone example, the resin is any of polymer resins produced by GE PLASTICS,Pittsfield, Mass., other plastic material produced by GE PLASTICS,silicones produced by GE SILICONES, Waterford, N.Y., or other flexibleresin-based rubber compounds produced by other manufacturers.

The mixture of base resins with conductive materials makes the overallconductive material 22 conductive rather than insulative. The resinprovides structural integrity. The conductive fibers, conductivepowders, carbon nanotubes, or a combination thereof, are homogenizedwithin the resin during the molding process, providing the electricalcontinuity.

In one example, the conductive powders are formed from non-metals, suchas carbon or graphite and may also be metal plated. In another example,the conductive powders are metals such as stainless steel, nickel,copper, or silver, and may also be metal plated. In one example, theconductor fibers are nickel plated carbon fiber, stainless steel fiber,copper fiber and/or silver fiber.

The following provides examples of how insulating material 20 andconductive material 22 are formed in assembly 10. Insulating material 20is formed by injecting insulating material into a mold to establish theshape of insulating material 20 over integrated circuit 11. Conductivematerial 22 is formed by injecting a mixture of resin and conductivematerials into a mold to establish the shape of conductive material 22.In one example, the conductive materials are homogenized (i.e., made anapproximately uniform consistency) within a base resin when molded overinsulating material 20. In an example, conductive material 22 is cut,stamped, extruded, laminated, and/or milled to provide the desired shapeand size. Conductive material 22 is applied using a syringe.

In one example, conductive material 22 also serves as a heat sink toabsorb heat generated by integrated circuit 11 to reduce the likelihoodof overheating by integrated circuit 11. In one example, conductivematerial 22 may inhibit x-ray probing of integrated circuit 11 andthereby inhibit attempts to determine the integrated circuit devicelayout.

Conductive contacts 24 are formed on inside upper surface 13 of package12 under the outer edges of conductive material 22. A conductive contact24 is provided to input a current to conductive material 22. An outputconductive contact 24 is provided to receive a current from conductivematerial 22. Multiple complementary conductive contacts are provided totransfer current through the conductive material. A single conductivecontact 24 can provide current (or other signal) that is measured by oneor more other conductive contact(s) 24.

During manufacture of assembly 10, impedances through portions of theconductive material 22 are measured. Direct or alternating current canbe applied through conductive material 10 using a conductive contact 24and received through one or more other conductive contacts 24. Theimpedance measured is a reference impedance value for the portion ofconductive material 22 through which such current flows. For example, aresistance, an inductance and/or a capacitance are measured. Theimpedance values measured using currents received by each conductivecontact 24 can be stored as reference impedance values in a memorydevice accessible to integrated circuit 11. The impedances can bemeasured for particular ambient temperatures and a table can be used toindicate the reference impedance values for each temperature.

Integrated circuit 11 includes an analog control circuit (not shown) toissue a current to conductive material 22 and an analog switch (e.g.,de-multiplexer) (not shown) to control which conductive contact 24issues the current. Integrated circuit 11 uses an analog switch (e.g.,multiplexer) (not shown) to control which conductive contact 24transfers received current for measurement by integrated circuit 11.

When assembly 10 is available for use by customers, integrated circuit11 compares the measured impedance value against a reference impedancevalue stored in memory. In one example, every few microsecondsintegrated circuit 11 issues a current (direct or alternating) throughone or more conductive contacts 24 and receives the current through oneor more conductive contacts 24. When the measured impedance valuediffers from the reference impedance value by a significant percentage,an indication of potential tampering is provided. One or more componentsof impedance (such as resistance, inductance, or capacitance) can bemeasured and compared with a reference resistance, inductance orcapacitance.

The temperature of conductive material 22 affects the impedance value ofconductive material 22. Integrated circuit 11 may include a temperaturesensor (not depicted) to measure the temperature of integrated circuit11. Mechanical proximity of conductive material 22 to integrated circuit11 means that temperature measured by the temperature sensor can be usedas the approximate temperature of the conductive material 22. Integratedcircuit 11 can adjust a reference impedance value of the conductivematerial based on the approximate temperature. In turn, smaller changesin impedance can be associated with tampering. Were temperature of theconductive material 22 not taken into account, larger changes in theimpedance of conductive material 22 would be used to trigger anindication of tampering and accordingly some tampering may not bedetected.

In one example, the indication of tampering causes a memory that storessensitive information (such as encryption keys or customer information)to be erased. In one example, the indication of tampering is provided bystoring the indication in memory of the integrated circuit. Otherindications can include communicating to a server computer thattampering has occurred such that the device that uses the assembly 10(such as a point of sale device) is disabled.

FIG. 2A is a simplified, cross-sectional, top-down view of assembly 10of FIG. 1. This view shows an arrangement of conductive contacts aroundthe perimeter of the conductive material 22. Conductive contacts 24would not be visible from the top-down view because conductive contacts24 are covered by conductive material 22. In one example, an intruderattempts to access the integrated circuit by forming a hole inconductive material 22. The hole changes impedance properties ofconductive material 22. Currents are transferred between various ones ofconductive contacts 24 and impedances are measured. For example, theimpedances through routes A and B are measured. A change in one of theseimpedances is detected and intrusion is indicated.

FIG. 2B is a simplified, cross-sectional, top-down view of an assembly30, in accordance with an embodiment of the present invention. Assembly30 is similar to assembly 10, except that rather than forming acontinuous region of conductive material 22, conductive material 22′ isformed in strips over and/or embedded in insulating material 20. In thisembodiment, conductive contacts 24 contact opposite ends of each stripof conductive material 22′. Measurement of signals transmitted throughstrip C can be used to detect a hole cut by an intruder. The spacingbetween adjacent strips of conductive material 22′ is made small enoughso that physical intrusion using standard probing equipment can bedetected.

FIG. 3 is a simplified cross-sectional side view of an assembly 40 witha conductive material provided in criss-crossing strips for use todetect access to the integrated circuit. In this embodiment, insulatingring 48 is formed around integrated circuit 11. In this example,insulating ring 48 does not contact integrated circuit 11. Connectors 50are formed inside insulating ring 48 and are positioned withininsulating ring 48 for alignment with vias 49 inside package 12. In oneexample, ring 48 is made of a ceramic material. Accordingly, connectors50 are conductively coupled with vias 49 to transfer signals betweenvias 49 and conductive contacts 52. Integrated circuit 11 issues signalsfor transmission through microbumps to a landing pad 16, through a via49 to connector 50, and ultimately to conductive contact 52. A lowerlayer 44 includes rows of strips of conductive material 42 formed amonginsulating material. An upper layer 46 is similar to lower layer 44,except the direction of strips is perpendicular to strips of lower layer44. A middle layer of insulating layer separates lower layer 44 fromupper layer 46. Although not depicted, some of connectors 50 extendthrough the middle layer to conductively couple vias 49 to conductivecontacts 52 of upper layer 46. Conductive material 42 can be the same asthat used for the assembly 10.

FIG. 4 is a simplified top-down view of the assembly of FIG. 3, inaccordance with an embodiment of the present invention. FIG. 4 showsthat connectors for upper layer 46 are formed along opposite inner edgesof ring 48 whereas connectors for lower layer 44 are formed on otheropposite inner edges of ring 48. The connectors for upper layer 46extend longer than those for lower layer 44 to protrude through middlelayer of insulating material to upper layer 46. Conductive contacts 52for strips of conductive material are positioned to be in contact withconnectors 50.

FIG. 5 depicts a simplified cross-sectional diagram of an assembly 60,including an integrated circuit 11 with a conductive plate 62.Conductive plate 62 enables the detection of access to integratedcircuit 11 when conductive plate 62 is cut. As for assembly 40,insulating ring 48 includes connectors 50 formed on the inside edges ofinsulating ring 48. In one example, plate 62 is a metal plate, andconductive contacts 64 are formed to contact plate 62 around theperiphery of plate 62, where the periphery extends at least beyond edgesof integrated circuit 11. Conductive contacts 64 align with connectors50 to form a conductive coupling. In another example, plate 62 is aceramic material with fine metal strips embedded so that each strip hasa conductive contact 64 at each end. Instead of metal strips, conductivematerial as described with respect to assembly 10 can be used.

FIG. 6 depicts a simplified cross-sectional diagram of an assembly 70,including an integrated circuit 74 with a conductive material 72provided to detect access to integrated circuit 74. In this embodiment,conductive plugs 76 protrude from the top of integrated circuit 74 andthrough a layer of insulating material to contact conductive material72. The layer of insulating material separates integrated circuit 74from conductive material 72. The layer of insulating material can be anoxide layer formed over the top of integrated circuit 74. In oneexample, conductive plugs 76 are formed around the periphery ofconductive material 72. Conductive material for conductive material 72can be the same as that described with respect to assembly 10 or anyother embodiment. In another example, conductive material 72 is stripsof conductive material as described with regard to FIG. 2B, andconductive plugs 74 contact ends of the strips. Integrated circuit 74measures changes in properties of conductive material 72 by providing asignal through one or more conductive plug 76 and measuring the signalreceived at one or more other conductive plugs 76. For example, animpedance can be measured and compared to a reference impedance value todetect tampering with conductive material 72.

FIG. 7 is a simplified cross-sectional view of point of sale device. Forexample, the device of FIG. 7 can be used in an automated teller machineor a credit card reading device. FIG. 7 shows that a mesh 200 is used tocover the top side of integrated circuit (IC) 201, memory 202, andbattery 203. Another mesh 204 is used to cover the underside of theintegrated circuit 201, memory 202, and battery 203. Integrated circuit201 detects tampering with either mesh. Each mesh includes many pairs ofvery fine wires or conductors. The wires of each such pair extend in aserpentine fashion in parallel. If any of the wires is broken, then thiscondition is detected by the integrated circuit. Also, if any part ofthe first of the wires touches any part of the second of the wires, thenthis condition is detected by the integrated circuit. Accordingly, if athief were to attempt to probe any device by pushing a probe through themesh, then the probing would likely cause a first wire to touch a secondwire, and this tamper condition would be detected. If the thief were toattempt to drill a hole in the mesh to obtain access for a probe, thistamper condition would also be detected.

In this embodiment, integrated circuit 201 includes a conductivematerial 205 formed over its surface to detect access to the integratedcircuit. Application of conductive material 205 can be accomplishedusing any of the embodiments described herein. Detection of tamperingcan occur using any of the embodiments described herein. Accordingly,use of mesh and conductive material provides redundant tamperingcapabilities.

The point of sale device of FIG. 7 can be used in connection with afinancial transaction. Consider an example of a transaction with a debitcard. A customer presents the debit card to the cashier of a store. Thecashier swipes the magnetic stripe on the card through a magnetic cardreader on the point of sale terminal. The magnetic card reader reads anaccount number encoded in the magnetic stripe of the card. The customerthen, for identification purposes, typically enters a personalidentification number (PIN) into a keypad device coupled to the point ofsale terminal. The customer may also enter other identificationinformation. The point of sale terminal then uses an encryption keystored in the point of sale terminal to encrypt the account number (fromthe swiped debit card), the identification number (for example, the PINnumber), and other information about the transaction such as the amountof the transaction and the date of the transaction. The encryptedinformation is sent from the point of sale terminal to the financialinstitution via a modem or other electronic communication link. Thefinancial institution receives the encrypted information and uses anencryption key to decrypt the information and recover the accountnumber, identification information, and information about thetransaction. In the case where the transaction is a debit transaction,the bank account of the customer is debited. A confirmation of thetransaction is then encrypted using the encryption key and the encryptedconfirmation is communicated from the financial institution back to thepoint of sale terminal. The point of sale terminal uses the encryptionkey stored in the point of sale terminal to decrypt the confirmation.

Thieves attempt to access sensitive information of customers, such aspreviously stored account numbers and personal identification numbers,and sensitive information of the point of sale device, such asencryption keys. The techniques described herein may prevent access tothis sensitive information. For example, sensitive information may bestored in SDRAM 202. In response to detecting intrusion, the SDRAM iserased.

FIG. 8 is a flowchart of a method that can be used to detect access toan integrated circuit in accordance with an embodiment of the presentinvention. In action 102, an insulating region is formed over or aroundan integrated circuit. The insulating region can be provided using amolding technique. The insulating region can be that described in any ofor a combination of any embodiment described with regard to figuresherein. In action 104, a conductive material is provided over theinsulating region. The conductive material can be provided using a mold.The conductive material can be that described in any of or a combinationof any embodiment described with regard to figures herein. For example,the conductive material can be a mixture of resin and conductive fibersor powders. In action 106, conductive coupling is provided between theintegrated circuit and conductive material. For example, conductivecoupling can take the form of connectors, conductive contacts, and/orplugs formed in or in contact with the insulating region and theconductive material as described with any embodiment. In action 108,characteristics of the conductive material are measured and stored asvalues into a memory. The memory is accessible to the integratedcircuit. For example, impedance (e.g., resistance, inductance, and/orcapacitance) measured for a direct current or alternating currentapplied through at least one conductive contact is stored in the memory.In action 110, access is monitored by detecting a change in acharacteristic of the conductive material measured between two or moreconductive contacts. In one example, the integrated circuit causescurrent to flow between two or more conductive contacts by way of theconductive couplings. An impedance (e.g., resistance, inductance, and/orcapacitance) is then measured for current received at one or moreconductive couplings. The measured impedance is compared with the storedexpected impedance associated with the relevant one or more conductivecouplings. In one example, temperature of the integrated circuit istaken into account to determine the expected impedance measured by wayof one or more conductive coupling. If the measured impedance issignificantly different from the expected impedance, then the assemblyis considered to have been tampered with and the memory that storessensitive information is erased.

Although some embodiments of the present invention have been describedin connection with certain specific embodiments for instructionalpurposes, the present invention is not limited thereto. In anotherexample of assembly 10 of FIG. 1, the insulating material is an oxidelayer formed over integrated circuit 11 during fabrication of integratedcircuit 11. In one example, the impedance through conductive materialcan be non-uniform. In another embodiment of FIG. 1, the circuitry isfabricated on the side of integrated circuit 11 facing away from insideupper surface 13 and microbumps of integrated circuit 11 face away frominside upper surface 13 such that conductive leads conductively couplethe microbumps to conductors on package 12 by extending from theperiphery of integrated circuit 11. In one example, conductive material22 can be formed from fibers or textiles that are then woven or webbedinto a conductive fabric. In one example, the memory that stores thereference impedance values is different from the memory that storessensitive information. The memories may be different storage arrays oreven memory types, i.e., flip-flops as opposed to SRAM. In one example,the conductive loaded resin-based material is formed in strips andinterwoven. In one example, rather than forming strips of conductivematerial 22′, a spiral and/or serpentine pattern is provided. In oneexample of the embodiment of FIG. 6, the integrated circuit 74 has itsactive circuit side facing toward the conductive material and conductiveleads from integrated circuit 74 are coupled to conductive receiversoutside of the periphery of the integrated circuit 74. In FIG. 7,instead of using mesh, the resin-based conductive material can be used.

In one example, in addition or as an alternative to measuring animpedance, a natural resonating frequency of the conductive material canbe measured to determine an expected resonating frequency. Subsequently,the natural resonating frequency of the conductive material can bemeasured again and compared with the expected natural resonatingfrequency of the conductive material. If the measured and expectedfrequencies differ, then a determination is made that tampering with theassembly has occurred. A voltage or current can be propagated throughthe conductive material to determine the natural resonating frequency.

Accordingly, various modifications, adaptations, and combinations ofvarious features of the described embodiments can be practiced withoutdeparting from the scope of the invention as set forth in the claims.

1. An apparatus comprising: an integrated circuit device; and a moldedconductive material formed over the integrated circuit device, whereinthe molded conductive material comprises a resin-based conductor, andwherein an indication of an access to the integrated circuit device isbased in part on a measurement of a change of at least one property ofthe molded conductive material.
 2. The apparatus of claim 1, furthercomprising: an electrically insulating region, wherein the electricallyinsulating region separates the molded conductive material from theintegrated circuit device.
 3. The apparatus of claim 1, wherein the atleast one property comprises an impedance of a portion of the moldedconductive material.
 4. The apparatus of claim 1, wherein the moldedconductive material includes a conductive powder interspersed within aresin.
 5. The apparatus of claim 4, wherein the conductive powder isselected from a group consisting of: carbon, graphite, metal platedcarbon, metal plated graphite, stainless steel, nickel, copper andsilver.
 6. The apparatus of claim 1, wherein the molded conductivematerial includes a conductive powder and conductive fibers interspersedwithin a resin.
 7. The apparatus of claim 6, wherein the conductivefibers are selected from a group consisting of: nickel plated carbonfiber, stainless steel fiber, copper fiber, silver fiber and carbonnanotubes.
 8. The apparatus of claim 1, further comprising: an inputcontact and an output contact, wherein an electrically conductive paththrough the molded conductive material couples the input contact withthe output contact. 9-10. (canceled)
 11. An apparatus comprising: anintegrated circuit; and means for indicating a tampering with theintegrated circuit, wherein the means comprises an homogenizedconductive material molded over the integrated circuit, wherein themeans indicates the tampering by detecting a change in a property of aportion of the homogenized conductive material, and wherein thehomogenized conductive material comprises a conductive thermoplastic.12. The apparatus of claim 11, wherein the property of the portion ofthe homogenized conductive material is an impedance of the portion. 13.The apparatus of claim 11, wherein the homogenized conductive materialis molded over the integrated circuit in at least one strip.
 14. Theapparatus of claim 11, wherein the homogenized conductive materialincludes a second material interspersed within a resin, and wherein thesecond material is selected from a group consisting of: a conductivepowder and conductive fibers.
 15. The apparatus of claim 14, wherein aconstituent of the conductive powder is selected from a group consistingof: carbon, graphite, metal plated carbon, metal plated graphite,stainless steel, nickel, copper and silver.
 16. The apparatus of claim14, wherein the conductive fibers are selected from a group consistingof: nickel plated carbon fibers, stainless steel fibers, copper fibers,silver fibers and carbon nanotubes.
 17. A method comprising: indicatingan access to an integrated circuit device based in part on a change ofat least one property of molded homogenized conductive material that isdisposed over the integrated circuit device.
 18. (canceled)
 19. Themethod of claim 17, wherein the molded homogenized conductive materialcomprises a conductive powder homogenized within a resin.
 20. The methodof claim 17, wherein the molded homogenized conductive material is aresin that contains a conductive powder, and wherein the moldedhomogenized conductive material is disposed over the integrated circuitdevice in at least one strip.
 21. The method of claim 17, furthercomprising: erasing a memory that stores confidential information inresponse to the indicating of the access.
 22. The method of claim 17,wherein the molded homogenized conductive material comprises conductivefibers homogenized within a resin.
 23. The method of claim 17, whereinthe property is taken from a group consisting of: an impedance through aportion of the molded homogenized conductive material, a current throughthe portion, a resistance of the portion, an inductance of the portionand a capacitance of the portion.